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United States Patent O 3,404,393 ALARM SYSTEM Sidney L. Blivice, 6247N.3Monticello, Chicago, Ill. 60645, and David J. Cohen, Chicago, Ill.(3838 W.

Jerome, Skokie, Ill. 60076) t Filed Apr. 1, 1965, Ser. No. 444,568 47Claims. (Cl. 340-276) The present invention has its most importantapplication to burglar alarm systems for buildings of various kinds,although certain aspects thereof have application to other alarmsystems, such as tire alarm systems. The most important application ofthe invention, however, is in burglar alarm systems for high-riseapartment buildings.

It is well known that burglary is becoming an increasingly seriousproblem, Burglary of high-rise apartment buildings is a particularlyserious problem. To be most effective, burglar alarm equipment should betied in with a watch service, and it should be easy for the apartmentoccupant to turn the burglar alarm system on and off when he goes in andout of the apartment without setting olf false alarms and withoutadversely affecting the security of the alarm system. Burglar alarmequipment has been rarely installed in high-rise apartments because ofthe high cost of the available equipment and/or because such equipmenthas had many functional deficiencies which make it impractical orineffective for use by the ordinary apartment occupant.

In high-rise apartments the principal point of entry into an unoccupiedapartment is through the doors thereof. Expert burglars have become veryadept at picking the locks of these doors (i.e. only about ten secondsare required to pick many of these locks). The simplest system formonitoring these apartments is to monitor the unauthorized opening ofthe doors thereof, but such a system must distinguish between theopening of the door by the occupant and an unauthorized person in amanner which does not adversely affect the security of the system, andit should be of a relatively low cost to install.

One of the objects of the invention is to provide a burglar alarm systemwhere an alarm is given by the unauthorized entry of a person throughthe door or window of any apartment and wherein the burglar alarm systemprovides maximum security at a reasonable cost. Another related objectof the invention is to` provide a burglar alarm system as just describedwherein the occupant can, in a very simple manner, set the alarm intooperation when he leaves the apartment and wherein, upon return to theapartment, the burglar alarm system can be readily disabled before falsealarm is given in a manner which does not adversely affect the securityof the system.

Another object of the invention is to provide a burglar alarm systemwhich provides a higher degree of security at lesser cost than burglaralarm systems heretofore developed.

A further object of the invention is to provide a burglar alarm, realarm or other alarm system for an apartment house, oice building or thelike, which utilizes existing wiring of the building, as, for example,the usual talk, listen, door solenoid and doorbell lines of a high-riseapar-tment building, and where this wiring of the building is usedsimultaneously for its normal function as well as for the added alarmfunctions without interference or interaction between the same. Arelated object of the present invention is to provide an alarm system asdescribed which can be applied to old or new buildings at a modest cost.

A still further object of the invention is to provide an alarm system asabove described where additional alarm or signalling systems can besuperimposed thereon at any time at a very modest cost. Thus, inaccordance with one aspect of the invention, a garage calling systemreadily can be incorporated into a burglar alarm system of the presentinvention at a minimum cost.

Another object of the invention is to 'provide a relatively inexpensivealarm system which is substantially tamper-proof.

Where the invention is applied to a burglar alarm system of an apartmentbuilding, two or more switches are wired into each apartment, one of theswitches being an entry sensing switch like a door switch which isoperated to an alarm position when the door is opened and an inoperativeposition when the door is closed. Although it is common in high-riseapartments to have only one entry door, if additional points of entryare to be monitored in the form of windows or doors, an additional entrysensing switch like the door switch referred to is added and connectedin a parallel circuit with the door switch referred to for each entrypoint to be monitored. l

Another of the switches is preferably a key operated switch mostadvantageously accessible on the outside of a -control box in eachapartment holding various components and terminals constituting thatportion of the burglar alarm system other than the door switch locatedin each apartment. The key switch includes a key operated lock whichtakes a much longer time to pick (such as one minute) lthan the usualkey operated lock used on the front door of the apartment involved. Thekey f' switch has a burglar alarm preparing position which prepares thealarm system in the apartment for operation and a burglar alarm turn-offposition which renders the burglar alarm system of the apartment in aninoperative position. When an occupant leaves his apartment with its keyswitch in the burglar alarm preparing position, as the door to theapartment is then opened by the occupant, the door switch is operated toits alarm position. A counter is provided for each apartment whichresponds to the door switch or other entry sensing switch by providingan alarm signal every two times an entry is made to the apartment sothat the alarm is not set off when the occupant leaves the apartment.The next (second) time an entry is made to the apartment, lthe counterinitiates an alarm signal which will energize: an audible alarm and aline extending to a watch service after a short time delay (like 30seconds) unless the key switch is operated to its alarm turn-olfposition within the delay period. Since this period is less than thetime it would take a burglar to pick the lock on the key switch, theentry of a burglar into the unoccupied apartment (or an occupiedapartment where the occupant had opened the door once before retiringfor the night) would trip the alarm system.

In the preferred form of the invention, a tamper switch is incorporatedin the control box of each apartment which switch will immediatelyinitiate an alarm if anyone opens the control box.

Still another feature of the invention is the provision of a testcircuit which indicates an audible alarm-in each apartment as amonitored door or window is opened and remains open provided the keyswitch is in its burglar alarm preparing position and the system isotherwise operating properly. The absence of such a signal thusindicates to an occupant leaving his apartment that he either forgot toprepare the alarm system for operation or that the system is defective.Since the audible alarm will be sounded also for an unauthorized entryas long as the door or window involved remains opened, such an alarmcould frighten a would-be burglar away. The test circuit may comprise aset of contacts of the key switch connected in series with a test buzzerand the door switch between two common lines across which a test powersupply is connected. Thus, as the occupant walks out of his apartment,if the key switch is in its alarm preparing position, the door switchwill close to energize the test buzzer as long as the door remains open.

Control pulses of a given pulse repetition rate but of different phaseare fed to the common lines to which the key and entry sensing switchesare connected so that pulses are fed to the individual doorbell lines atvarious reference times each cycle to be hereinafter referred to astimes t1 and t2. Thus, if the key switch of an apartment is operated toits alarm preparing position, pulses at, say, time t1 cyclically appearon the associated doorbell of the apartment involved. If the door to anapartment is opened, control pulses cyclically appear on the doorbellline of the apartment involved at, say, time t2.

One of the important aspects of the invention is the manner in which theburglar alarm system is superimposed on the common wiring in thebuilding involved to minimize wiring costs. In the preferred form of theinvention, the burglar alarm system uses common and individual wiringalready used in various signalling circuits to connect the variousaforementioned key, door and tamper switches to a central annunciatorcontrol station. The common and individual wiring is most convenientlythe conventional common door solenoid, listen and talk lines extendingbetween the various apartments and the entrance hallway of the apartmenthouse, and the individual doorbell lines respectively extending to thevarious apartments. In this regard, it is common to provide in theentrance hall of an apartment house individual doorbell pushbuttonswitches connected through individual doorbell lines extending to thevarious apartments where closure of a switch operates the doorbell inthe selected apartment. The entrance hallway also frequently has atelephone transmitter unit connected by a common listen line to`receiver units in all the apartments for enabling a visitor to conversewith the occupant of an apartment, and a receiver unit connected by acommon talk line to the transmitter units in all the apartments toenable the visitor to hear the occupant of the apartment involved.Entrance to the interior of the apartment house is usually blocked by anentrance door on an inside wall of the entrance hall- A solenoidoperated lock is usually provided for locking the entrance door untilthe occupant of an apartment presses a solenoid pushbutton switch whichreleases the lock to the door.

In the most preferred form of the present invention, a set of contactsof each door switch is connected through an isolating rectifier betweenone of the aforesaid common lines referred to and the doorbell line ofthe apartment involved. A set of contacts of each key switch areconnected through an isolating rectier between another of the commonlines and the doorbell line of the apartment involved.

It is desirable to provide -a tamper switch on each control box so thatany opening of the box will initiate an alarm. Where a tamper switch isused, a set of contacts thereof is connected through an isolatingrectifier between still another one of the common lines to which controlpulses of a third t3 phase are fed to the associated doorbell line.Where a tamper switch is closed due to the opening of the panel on thecontrol box referred to, control pulses having a t3 phase will appear onthe associated doorbell line.

Thus, the presence of a first series of control pulse having a t1 phaseon any given doorbell line indicates that the apartment involved isbeing monitored. The presence of a first series of control pulses on adoorbell line having a t2 phase indicates that the door involved hasbeen opened once, and the presence of a second series of control pulseshaving a t2 phase on a doorbell line indicates that the door has beenopened a second time. The presence of control pulses having a t3 phaseon a doorbell line indicates that the control box in the apartmentinvolved has been opened.

There is located at a central annunciator station in the buildinginvolved (usually in the building basement) a logic annunciator circuitfor each apartment which responds to the various pulses on theassociated doorbell line in the following way: The presence of pulseshaving a l1 phase resulting from the operation of the key switch of theapartment to its alarm preparing position will activate a counter of theapartment involved so that presence of two spaced series of pulseshaving a t2 phase indicating two successive openings of the apartmentdoor will initiate an alarm control signal which will result in thesounding of an audible alarm to alert the manager of the buildinginvolved and the signalling of a watch service or police stationprovided the t1 phase pulses on the doorbell line involved do notdisappear within the time delay period referred to previously.

The presence of pulses at time I3 due to the operation of the tamperswitch to an alarm position will immediately effect an alarm for thatapartment involved independently of the position of the associated keyswitch. In this manner, close control is kept over the opening of thecontrol box and maid help or others could not tamper with the controlbox while the key switch happened to be in a burglar alarm turn-offcondition and disable the equipment without setting off an alarm. Whenauthorized personnel are to gain access to the control box, notice ofthis fact will be given to the building management as well as a watchservice so that any alarm will be ignored during the access period.

Still another aspect of the invention deals with the provision of asupervision control over the individual lines carrying the controlsignals from the various apartments, such as the doorbell lines. Pulsesat a special reference phase, such as a time t4 each cycle arecontinuously coupled through a common line and an isolating rectifier ineach apartment to each doorbell line, An annunciator circuit is providedat the aforesaid control annunciator station which gives adistinguishing alarm for the apartment involved when the 14 pulses areabsent from a doorbell line evidencing the severing of a doorbell lineor other defect in the `alarm system.

Other aspects of the invention, including the manner in whichinteractions between the signalling circuits of the apartment buildingand the monitoring system of the invention superimposed thereon areminimized or prevented will be described in the specification to follow,Also, it will be appreciated that some aspects of the invention areapplicable to individual homes and to fire alarm Aand other monitoringsystems.

In the drawings:

FIGS. lA and 1B together form a partial wiring diagram of an apartmenthouse showing the wiring normally found therein and the exemplaryburglar alarm system of the present invention superimposed thereon;

FIG. 2 is a cross-the-line diagram of part of the system shown in FIGS.lA and 1B;

FIG. 3 is timing diagram showing various timing voltages utilized in theembodiments of FIGS. 1 and 2;

FIG. 4 is a basic block diagram of the annunciator circuit associatedwith each apartment;

FIG. 5 is a front View of the central enclosure which houses many of thebasic components making up the annunciator and timing circuits;

FIG. 6 is a side View of the enclosure of FIG. 5;

FIG. 7 is a more detailed diagram of the logic circuit elements makingup the annunciator circuit shown in FIG. 4;

FIG. 8 is a fragmentary view of FIG. l with a garage calling systemadded thereto;

FIG. 9 shows the logic circuit elements which are tied in with thecircuit shown in FIG. 8 to complete the garage calling circuit; and

FIG. l0 is a circuit diagram for a part of the logic circuit shown inFIG. 5.

GENERAL DESCRIPTION Referring to FIGS. 1A and 1B which include a typicalwiring diagram for the communication doorbell and door openingsignalling circuits for a high-rise apartment building. These signallingcircuits extend between the entrance hall (FIG. 1A) of the building andvarious apartments identitied by numbers 1, 2, etc. As is common, theentrance hall has an entrance door (not shown) on an inner wall thereofwhich blocks entrance to the interior of the apartment building beyondthe entrance hall. The door is normally kept in a locked position by alock operated by a solenoid 13. When the solenoid is energized, the lockis released which permits the door to beopened.

The bottommost terminal of the solenoid 13 in FIG. 1A is connected to acommon front door solenoid line 14' extending to a terminal board 17 inthe basement. A continuing section 14 of the common solenoid linesextend from the terminal board to the various apartments throughindividual branch lines 14-1, 14-2, etc. Normally, the branch lines14-1, 14-2, etc. extend directly to the respective door solenoidoperating pushbutton switches 16-1, 16-2, etc. in the various apartmentswhich, when operated, place building ground on the line 14. However, inthe present invention the branch lines 14-1, 14-2, etc. extend throughisolating rectiers 17-1, 17-2, etc. in alarm control boxes 18-1, 18-2,etc. in the respective apartments. The alarm control boxes containvarious circuit elements to be dtscribed and all of the special burglaralarm wiring found in each apartment (except for a door switch to bedescribed) which in conjunction with the conventional wiring extendingbetween the apartments entrance hall and basement and other specialcomponents preferably located in the basement of the building, completethe burglar alarm system.

Normally, the solenoid 13 is designed to operate on either alternatingcurrent or direct current, alternating current being the most commonlyused source of power for'operation of the solenoid 13. However, in thepreferred form of the invention, the upper terminal of the solenoid 13is conected through a line 20 and a relay contact F1 (FIG. 1B) or otherswitch to the negative terminal 24 of the direct current building powersupply generally indicated by reference numeral 26. It should beunderstood that the present invention is not limited to the use of anyparticular power supply, but in the embodiment of the invention to beillustrated, the terminal 24 will be assumed to have a negative voltage,such as a negative 14 volts DC, with respect to building ground B.(Building ground is utilized to indicate a reference or ground pointwhich is different from another ground point to be referred to as logicground L.)

As will appear, the switch F1 is opened and closed for equal half cycleintervals at a relatively low fre quency, such as 100 cycles per second.The closure time of the switch F1 and the frequency at which the switchis opened and closed is adjusted so that the average direct voltageappearing on the line will provide the necessary voltage to operate thedoor solenoid 13 when any door solenoid switch 16 is closed.

Also located in the entrance hall 10 are individual doorbell ringingpushbutton switches 28. Each of the doorbell switches has one terminalconnected to an individual doorbell line 30-1', 302, etc. extendingthrough isolating rectiers 31 to the basement terminal board 17 andthrough an extension line 30-1, 30-2, etc. to the particular apartmentinvolved. In FIG. lA doorbell line 30-1 extends to apartment No. 1 anddoorbell line 30-2 extends to apartment No. 2, etc. The individualdoorbell lines respectively extend through isolating rectiiiers 29-1,29-2,l etc. in the respective control boxes 18-1, 18-2, etc. to thedoorbells 31-1, 31-2, etc. which are connected to building ground. Theother terminals of the doorbell switches 28 areconnected by a commonline 33 through an oscillating switch F2 opening and closing with theaforesaid switch F1 to the positive terminal 35 of the building powersupply 26.

`In the exemplary form of the invention, the voltage on the terminal 35may be, for example, 20 volts positive with respect to building groundB. Assuming the switch F2 will be opened and closed for equal intervals,the

average voltage on the common line 33 will be roughly 10 volts, which issufficient to energize the usual doorbells. It is assumed that thedoorbells 31 are conventional doorbells designed to operate on 60 cyclesA.C. current. When the present invention is utilized in an alreadyexisting building having such doorbells, the periodically interrupteddirect current on the common line 33 will operate such A C. doorbellssince the armatures of the doorbells are designed to oscillate atfrequencies in the neighborhood of 60-120 cycles per second.

As will appear, the present invention utilizes individual control linesassociated with the apartments, such as the doorbell lines 30, forcarrying various control signals to annunciator circuits to be locatedpreferably in the basement of the building.

In addition to the front door solenoid line 14, which is in common withall of the apartments, FIG. 1A shows three other common lines, namely acommon listen line 32, a common talk line 34, anda rear listen line 36.The listen line 32 is connected to branch lines 32-1, 32- 2, etc. tonormally open manual switches 33-1, 33-2, etc. connected to groundedreceiver units 40-1, 40-2, etc. in the various apartments. The listenline 32 extends to the terminal board 17 in the basement and anextension line 32 to the bottom terminal of a transmitter unit 38 in theentrance hall 10 which enables a. visitor to talk to an occupant of anapartment. The upper terminal of the transmitter unit 38 is connected bya line 42 to a positive terminal 45 on the building power supply. Theusual direct current voltage for operating the varous transmitters andreceiver units is present on the terminal 45. The terminal 45 of thebuilding power supply may, for example, be in a positive voltage of 16volts DC with respect to building ground.

The talk line 34 is connected by branch lines 34-1, 34-2, etc. tonormally open manual switches 33-1, 33-2, etc. connected to groundedtransmitter units 48-1, 48-2, etc. in the various apartments. The talkline 34 extends to the terminal board 17 inthe basement land through anextension line 34 to the bottom terminal of a receiver unit 44 in theentrance hall whose upper terminal is connected to the common line 42leading to building power supply terminal 45.

As previously indicated, when t-he occupant of a building hears theringing of his doorbell, he goes to the location of his transmitter andreceiver units 48 Vand 40 and presses ya pushbutton or the like whichsimultaneously closes the switches 33-1 and 33-1'.

In the apartment building being described, in addition to a frontentrance hall 10 there is a rear entrance 10 with similar communicatingunits, such as .a transmitter unit 38. The aforementioned rear listenline connects with the bottom terminal of the transmitter unit 3Sthrough the basement terminal board 17 and extension line 36'. The upperterminal of the receiver unit is connected to the power supply conductor42 leading to the power supply terminal 45.4 The rear door listen line36 is connected by branch lines 36-1 and 36-2 to respective manuallyoperable switches 49l, 49-2, e-tc. in the various apartments which areconnected to the ungrounded terminals of the receiver units 40-1, 40-2,etc. in the various apartments.

In a modern apartment building, the various common `and individual lines14, 30, 32, 34 and 36 are commonly carried in conduits embedded withinconcrete posts or risers extending down into the basement. In thepreferred form of the invention, the conduits extend to a largeenclosure 50 illustrated by .the dashed box 50 in FIG. 1B and shown inFIGS. 5 and 6, which enclosure has a key locked front door 51. Thebuilding power supply 26, the terminal board 17 and various annunciatorsand other components for the burglar alarm system are locked in thisenclosure. In a manner to be described, a normally energized conductor53 is closely 'wrapped over the entire exposed area of the enclosure 50and the door 51 thereof so that easy entry to the box requires severanceof the conductor and interruption of a supervisory current flowingtherein.

In the description to follow, reference should rst be made primarily toFIG. 2, which is a simplified acrossthe-line diagram of cost of thecircuitry shown in FIG. 1A and some of the circuitry shown in FIG. 1B.

In the illustrated form of the present invention applied to a high-riseapartment, there is provided in each apartment at least one entrysensing7 means for each entry point :to be monitored, such as a doorswitch DS-l or DS-Z, etc. an alarm preparing switch such as a key switchKS-l, or KS-2, etc. and a tamper switch TS-l or TS-2, etc. In thebroadest aspect of the invention, the switches could be electronicswitches or mechanical switches as illustrated. The mechanical switchesare open in their inoperative positions and closed in their operativecontrol signal producing positions as will appear from the descriptionto follow. In the claims, reference is made to a condition -of a switchwhich term generically will represent a state of a mechanical and/or anelectronic switch.) FIG. 2 also shows an additional entry sensing ordoor switch DS-l or DiS-2', etc. in parallel with each door switch andrepresents a back door, a window operated switch or the like whichoperates in the same way as the door switches DS-l and DS-Z, etc. Thus,each illustrated switch is closed when the door or wind-ow involved isopened and is open when the door or window is closed.

Each key switch KS as illustrated has two sets of contacts to berespectively identified by reference characters KS-la and KS-lb or KS-2aand KS-Zb, etc. Each key switch is provided with a key receiving lockexposed on the loutside of the control box 18-1 or 18-2, etc. of theassociated apartment. This lock is a much more expensive lock than t'helock normally used on apartment doors, so that it would take even anexpert burglar a much longer time to pick, such as a time in theneighborhood of one minute or longer. In the circuit being described,each of the key switch contacts will be open when the key switch is in anormal burglar turn-off position and will be closed when the key switchis turned to a burglar alarm preparing position.

The control box 18-1 or 18-2, etc. of each apartment is l-ocated in aposition such that the occupant entering by =a front or rear door could,without rushing, gain access thereto in a relatively short time which ismuch less than would be required for a burglar to enter the apartment bya window or door and then pick the lock of the key switch. The controlbox is most advantageously provided with a door (not shown) which in itsopened condition opens the associated tamper switch TS-l or TS-2, etc.and in its closed condition closes the tamper switch.

The key switch contacts KS-lb or KS-Zb, etc. are connected through anisolating rectifier 56 between the front listen line 32 and theassociated doorbell line. The rectier 56 is arranged to pass a positivevoltage appearing on the listen line 32 to the doorbell line. The entrysensing or door switch, such as DS-1 or DS-2, etc. of each apartment isconnected through an isolating rectifier 58 .and the key switch contactsKS-lb or KS-Zb, etc. between the front talk line 34 and the associateddoorbell line, the rectifier passing a positive voltage appearing on thetalk line 34. The tamper switch TS-l or TS-Z, etc. in each apartment isconnected through an isolating rectifier 60 between the front solenoidline 14 and the associated doorbell line, the rectifier passing apositive voltage appearing on the solenoid line 14. An isolatingrectifier 68-1 or 68-2 is connected directly between the rear listenline 36 and each doorbell line.

Each apartment includes a test circuit connected between two of thecommon lines, such as the talk and listen lines 34 and 32. Each testcircuit comprises a test buzzer 62-1 or 62-2, etc. located in eachcontrol box 18-1 or 18-2, etc. and associated key switch contacts KS-laor KS-Za, etc. connected in series with the associated entry sensing ordoor switch DS-l or DS-2, etc. Closure of this circuit connects theassociated buzzer across the lines Cit 32 and 34. A direct current testpower supply 63 mounted in the basement enclosure 50 is connected acrossthe c-ommon lines 32 and 34, the positive terminal thereof beingconnected to the talk line 34 and the negative terminal thereof beingconnected to the listen line 32. Thus, opening of a door or window inany apartment in which the key Switch is in a burglar alarm preparingposition will sound the associated test buzzer while the door or windowinvolved remains open unless there is a broken line or other failure inthe system.

In a manner -to be described, positive control pulses of the samenon-audible pulse repetition rate but of different phase arc fed to thevarious common lines 14, 32, 34 and 36 referred to. Due to thenon-audible rate of the pulses appearing on the talk and listen lines,the pulses will not be heard on the various receiver units referred to.Some isolation from these pulses is provided by utiliz ing a ground(logic ground L) isolated from building ground, but someinterconnections of these grounds can occur and so the non-audible ratefurther minimizes the problems of noise introduction into the talk andlisten lines. Thus, as shown in FIG. 2, a pulse generator circuit 70 isprovided with output terminals T1, T2, T3 and T4 at which positivepulses appear relative to logic ground L having the various phases shownin waveforms b, c, d and e `of FIG. 3 and referred `to as phases t1, l2,t3 and t4. The pulse generator also has an -output terminal T at whichreset `pulses having a phase to appear. The output terminals T1, T2, T3and T4 are respectively connected to the respective common lines 32, 34,14 and 36.

It is thus apparent that when any key switch KS is operated to itsburglar alarm preparing position, positive pulses (relative to logicground L) having phase t1, appear on the doorbell line of the apartmentinvolved. Likewise, when a monitored door or window of any apartment isopened resulting in the closure of the associate-d entry sensing switchDS, positive pulses having phase t2 appear on the associated doorbellline provided the associated key switch is in a burglar alarm preparingposition, and when the door to any of the control boxes 18 of anyapartment is opened, the associated tamper switch will close to couplepositive pulses having phase t3 to the associated doorbell line. Thepositive control pulses having the phase 14 on the common line 36 arecontinuously coupled through the isolation rectier 68 to the doorbelllines associated with each apartment.

As illustrated in FIG. 1B, the pulse generator circuit 70 includes anoscillator 71 connected to logic ground L and operating at a non-audiblepulse, a repetition rate, such as 20 kilocycles per second. The outputline of the oscillator 71 is fed to a conventional ring counter 73having output terminals 73-0, 73-1, 73-2, 73-3, and 73-4, at whichrespective pulses appear shown in waveforms a, b, c, d and e in FIG. 3at times to, t1, t2, t3 and t4 each cycle. The to phase pulses carry outa resetting operation in the annunciator system to be described indetail later on in the specification. The aforementioned outputterminals of the ring counter 73 are connected respectively to the baseelectrodes or switching transistors 75-0, 75-1, 75-2, 75-3 and 75-4whose emitter electrodes are connected to a positive terminal 77' of thelogic power supply 78, operating with respect to logic ground L. Thecollector electrodes of the aforementioned transistors are connected tothe aforesaid outputs terminals T0, T1, T2, T3 and T4 of the pulsegenerator circuit 70. At times, to, t1, t2, t3 and t4 of each cycle ofoperation of the ring counter, a gating voltage sequentially appears atthe output terminals thereof which effect momentary conduction of thetransistors 75-0, 75-1, 75-2, 75-3 and 75-4 which couples the positivevoltage of the power supply terminal 77' to the associated terminals T0,T1, T2, T3 and T4.

In a manner to be explained, a logic annunciator system to be describedis connected to the various doorbell lines to provide various alarmoperation, depending on the presence and absence of pulses of variousphases on the doorbell lines.

As previously indicated, the various common lines 32, 34, 14 and 36 areenergized from the building power supply 26 during the operation of thevarious doorbell, solenoid, and talk and listen switches in the entrancehall or the apartments. It is extremely important to avoid interactionbetween the signalling and annunciator circuits involved, suchinteraction being surprisingly possible under various circumstances(despite the use of isolating rectiers and isolated grounds in theabsence of features to be described through various circuit pathsextending) through the various apartments, power supplied, etc. Thesequential pulsing of the various common lines materially aids inpreventing such interaction, but other features are further needed to`minimize or eliminate this interaction.

'In accordance with another aspect of the4 invention, a switching systemis provided which alternately renders the signalling circuits and theannunciator system operative at a switching rate which is much lowerthan the pulse repetition rate of the pulses generated by the pulsegenerator circuit 70 so that a time sharing of the -building wiring isachieved which permits both the signalling and annunciator to operate.As illustrated, this switching system includes an oscillator 74 whichoperates, for example, at 100 cycles per second. This oscillatoralternately energizes and de-energizes relay F controlling theaforementioned contacts F1 and F2 to alternately connect and disconnectthe terminals 24"and 35 of the building power supply to and from theassociated common line 14 and the doorbell lines 30.

When the contacts F1 and F2 are closed to render the associatedsignalling circuits operative, it is important to disable the operationof the annunciator system, Accordingly, referring to FIG. 1B, the relayF has a set of contacts F3 which are open when contacts F1 and F2 areclosed and are closed when the latter contacts are open. The contacts F3alternately connect and disconnect the positive terminal 77 of the logicpower supply 78 to and from one of the inputs 80-0, 80-1, 80-2, 80-3 and80-4 of a series of AND gates 82-0, 82-1, 82-2, 82-3 and 82-4 havingsecond inputs 80-0, 801, S02, 80-3 and 80-4 respectively connected tothe output terminals T0, T1, T2, T3 and T4 of the pulse generatorcircuit 70. The AND gates couple control pulses on the latter terminalsonly when the gate inputs 80-0, 80-1, etc. receive a positive gatingvoltage through the relay contact F3. The control pulses coupled throughthe AND gates are fed and gating lines T', T1', T2', T3 and T4 to thevarious annunciator circuits 84-1, 84-2, etc. where they operate variouscircuits thereof to be described. The annunciator circuits cannotoperate in the absence of these pulses.

To realize the necessity of disconnecting the building power supply 26from the doorbell line 30 and the common line 14 while the annunciatorcircuits-are operable, it must be recognized (see FIG. 2) that interlineimpedance exists between the common listen line 32 and a doorbell linein the form of transmitter 38, when the associated doorbell switch 28 isdepressed, and between common solenoid line 14 and common line- 32 inthe form of solenoid 13 and transmitter 38 in series. It should furtherbe noted that an interline impedance exists between a first and a seconddoorbell line 30 in the form of the doorbell connected to the firstdoorbell line, when the doorbell switch 28 of the second doorbell lineis closed.

If the contact F2 were closed while the' annunciator circuit isoperative, and if the input impedance of an annunciator circuitconnected between a doorbell line 30 and logic ground L is much greaterthan the impedance ofthe transmitter 38, the t1 pulses at pulsegenerator-.terminal T1 will create a false signal on doorbell line bybeing coupled to said doorbell line of each apartment having itsassociated doorbell pushbutton .28 depressed through a path extendingthrough transmitter 38 into power supply 26, out of power supplyterminal onto line 33, through the F2 contactsthrough the closedpushbutton switch 28 and rectifier 31 of theapartment involved,irrespective of the condition of the associated key switch. Theundesirable path would of course be eliminated if contact F2 were open,or if the inherent interline impedance represented by transmitter 38 isnot present.

If the F2 contact is closed while the annunciator circuits areoperative, the key switch contact KS-lb of apartment No. 1 is closed,the KS-1b contact of apartment No. 2 is open, and the doorbellpushbutton switch 28 of apartment No. 2 is depressed, the t1 pulses atpulse generator terminal T1 will create a false signal for apartment No.2 by being coupled to the doorbell line of apartment No. 2 through apath extending through isolating rectilier 56, closed contact KS-lb,rectifier 29-1 and doorbell 31-1 of apartment No. l onto building groundB, through the building power supply 26, out of its terminal 35, ontoline 33, through the F2 contacts, through the closed pushbutton switch28 and the rectier 31 of apartment No. 2. This undesirable path would beeliminated if contacts F2 were open, or if the inherent interlineimpedance between doorbell lines represented by doorbell 31 is notpresent or is very large.

If the F1 Contact is closed while the annunciator circuits areoperative, the t3 pulses at pulse generator terminal T3 will initiate afalse alarm from an apartment having its associated key switch closed,by being coupled to the associated doorbell line of said apartmentthrough a path extending through solenoid 13, contacts F1, into powersupply terminal 24, through the building power supply 26, out of powersupply terminal 45, through the transmitter unit 38, onto the frontlisten line 32, through isolating rectifier 56 and the closed key switchcontact KS-lb of the apartment involved, irrespective of the conditionof the tamper switch contact TS of the apartment involved. Thisundesirable path would, of course, be eliminated if contacts F1 wereopen, or if the inherent interline impedance represented by solenoid 13and in series with transmitter 38 is not present or is very large.

In addition to the possible interactions between the signalling andannunciator circuits occurring through the building power supply whichare overcome by the switching system and other features previouslydescribed, interactions caused by mutual impedance and not involving thebuilding power supply in the form of the transmitter and receiver unit,between common lines can occur and feed control pulses between thecommunication lines 34 and 32, 34 and 36 and 32 and 36, creating falsealarm signals on the doorbell lines. Thus, in the absence of the testpower supply 63, if the input impedance of an annunciator circuitconnected between a doorbell line and logic ground is much greater thanthe combined impedance of the transmitter and receiver units 44 and 38(see FIG. 2), the t2 pulses at pulse generator terminal T2 are coupledto the doorbell line of each apartment having a key switch in an alarmpreparing (closed) position through a path extending through the frontentrance hall receiver and transmitter units 44 and 38, the front doorlisten line 32, isolating rectifier 56 and the closed key switchcontacts KS-lb of the apartment involved, said path forms a completecircuit because thedoorbell line connects to the annunciator circuitwhich connects back to logic ground L 'as does the pulse generator. Thisundesired result is alleviated by the test power supply 63 whichprovides a voltage output which is greater than the amplitude of thepositive pulses on the output thereof, and the positive terminal thereofis connected to the front door talk line 34 and the negative terminalthereof is connected to the front listen line 32. In such case, the testpower supply is effectively connected across the front entrance hallreceiver and transmitter units 44 and 38, forcing the voltage across theseries combination of said receiver and transmitter units to beidentical to the output voltage of test power supply 63. The t2 pulsesnow attempt to feed from logic ground L through the path extendingthrough the pulse generator 70 onto line 34 through the parallelconnection of the test power supply 63 and the series connectedtransmitter and re- 11 ceiver units 38 and 44, through isolatingrectifier 56, the closed contacts KS-lb of the apartment involved, andthe annunciator circuit impedance of the apartment involved. However,since the voltage of test power supply 63 is greater in magnitude thanthe voltage of the positive t3 pulses, and both of said voltages areconnected with opposing polarity in a series circuit path, the neteffective voltage of said series circuits is such as to backbiasisolating rectifier 56 against feed-through of the IZ pulses through themutual impedance effected by the series connected transmitter andreceivers 38 and 44. The test power supply 63 will have no efiect on therectifiers 56 with respect to the t1 phase pulses normally applied tothe front listen line 32, since the terminals of the test power supplyare not connected to effect the conduction of the isolating rectifiers56 during the presence of the t1 pulses on the line 32.

If the rectifiers 58 are connected directly to their doorbell lineinstead of through the alarm preparing switch contacts KS-la or KS-lb,etc. a t1 pulse will appear on each doorbell line even though theassociated key switch is in a burglar alarm turn-off position. This t1pulse will be fed from line 32 through the test power supply 63, intoline 34, and through each rectifier 58 to the associated annunciatorcircuit when the associated apartment door is opened, irrespective ofwhether the key switches KS-l, or KS-Z, etc. are set to the alarmpreparing position. Hence, the power supply 63 taken alone is notsufficient to prevent critical interactions between common lines 32 and34, but must be combined with the series connection of the door switchDS-l or KS-Z, etc. and the associated key switch KS-l or KS-Z, etc.,between lines 32 and 34.

In the absence of isolating power supply 63', the positive terminal ofwhich connects to the front talk line 34, and the negative terminal ofwhich connects to the rear listen line 36, the t1 pulses at pulsegenerator terminal T1 can also be coupled to the doorbell line through apath extending through the front entrance hall transmitter 38, rearentrance hall transmitter unit 38', the rear door listen line 36 andisolating rectifier 68. This undesirable result is alleviated by theisolating power supply 63 provided the output thereof is greater thanthe amplitude of the positive pulses on the listen line 32 added to theabsolute magnitude of the test power supply 63. In such case, theisolating power supply 63 is effectively connected in series voltageopposition to the positive voltage of the t1 pulse added to the testpower supply potential on line 34 applied with respect to logic ground.Thus in effect, isolating power supply 63 back-biases each isolatingrectifier 68 against feed-through of t1 pulses through t the transmitterunits 38 and 38. In a like manner, at time t2, isolating power supply63' back-biases isolating rectifier 68, thereby precluding feed-throughof l2 pulses via front receiver unit 44, and rear transmitter unit 38.

At time t4, the alternate path that could be provided by t isolatingpower supply 63 and either of the rectitiers 56 or 58 for the positivet4 pulses is of no consequence.

The isolating power supply 63 and the isolating feature ofthe test powersupply 63 are used to nullify the interaction caused by the interlincimpedance inherent in the normal building wiring. In other environmentsthis adverse effect may be overcome by employing means to disconnect allinterline impedance during the time the monitoring system is operating.

Associated with each of the annunciator circuits 84-1, 84-2, 84-3, etc.in the preferred form of the invention is a red alarm light 90-1, 90-2,etc., and a white alarm light 90-1', 90-2, etc. These lights are locatedpreferably either in the building managers otiice or, as illustrated inFIG. 5, within the enclosure where the pairs of lights -1, and 90-1',etc. are visible through pairs of windows 91-91' on the front door panel51. In a manner to be explained, when pulses appear at time l2 on anydoorbell line, representing a second successive penetration or openingof a door or other entry point of an apartment and the associated keyswitch which is not returned to its burglar alarm position within thedelay period previously described, the red light 90-1 or 90-2, etc. ofthe apartment involved will be energized. The white light 90-1 or 90-2,etc. associated with any apartment will be energized whenever the t4pulses disappear from the associated doorbell line at `time t4. Wheneither -a red or white light of an apartment is energized, an alarmsignal appears on a common alarm line 92 which is fed to the set inputterminals of an audible alarm bistable circuit 94 and a watch servicebistable circuit 96. The setting of these bistable circuits willrespectively sound an alarm 98 and deenergize a relay 100 both locatedwithin the enclosure 50. The sounding of an alarm 98 will attract thebuilding manager or engineer to the panel 51 on which the various lights90-1, 90-2, etc. are visible so that the location of the trouble can beimmediately pin-pointed. The de-energization of the relay 100 will closea set of normally closed contacts 102 which will energize a line,usually a telephone line extending to a police station or watch service.A common lamp reset pushbutton switch 104 is provided which, whendepressed, resets the annunciator circuits to turn-ofir any energizedlights 904, 90-1, 90-2, etc. A similar pushbutton switch 106 is providedfor resetting Ithe audible lalarm circuit 94 lto terminate the soundingof the horn 98, and a common manual reset pushbutton switch 108 isprovided for resetting the watch service bistable 96. The variouspushbutton switches 104, 102, and 106 may be located at any secureconvenient point, such as the inside of the enclosure 50 where an alarmwould be sounded if someone tried to gain access tothe resetplushbuttons. In the alternative, the pushbutton switches could beexposed and a tamper proof circuit could be added to the resetpushbutton switches of each apartment so that depression of any resetpushbutton switch in the absence of an alarm would itself set off analarm.

Although the details of the various annunciator circuits 84-1, 84-2,etc. will be described in detail later 0n in `the specification, it willbe helpful at this point to b'riey explain some of the lbasic componentsmaking up each annunciator circuit. For this purpose, reference shouldbe made to FIG. 4 which shows annunciator circuit 84-1. As there shown,an input line 30-1" connected with each doorbell line 30-1, or 30-2,etc. at the basement terminal board 17 (FIG. 1B) extends in common toone of the inputs of a tamper switch signal circuit 110, a key switchsignal circuit 112, a door switch signal circuit 114 and a supervisorysignal circuit 116. The tamper switch signal circuit 110 has a secondinput extending `to the gating line T3 of the pulse generator circuits70; the key switch signal circuit 112 has a second input extending tothe gating line Tl'; the door switch signal circuit 114 has a secondinput extending to the gating line T2 and a reset input extending to thegating line T0 and the supervisory signal circuit 116 has a second inputextending to the gating line T4. Each of the aforesaid second inputs ofthe signal circuits 110 and 116 act as a gating input which results inthe generation of a control signal at the output of the circuit involvedif the pulses at the gating input coincides with the presence or absenceof control pulses on the associated doorbell line.

The key switch signal circuit 112 has a third input connected to thegating line T0 of the pulse generator circuit which feeds the settingpulses at or near the beginning of each cycle to the key switch signalcircuit 112. The circuit 112 generates -a steady signal each cycle atthe output 124 thereof until it is reset at or near the beginning of thenext cycle, which signal indicating ythe position of the associated keyswitch. The door switch signal circuit 114 includes counter andintegrating elements to be described which responds `to groups of pulsesby providing a control signal at lthe output of the door switch circuitfor every two groups of spaced pulses fed thereto. The opening of a dooror window twice will result in two groups of spaced pulses because theperiod a door remains opened` as it is opened and elo-sed encompassesmany cycles of Vthe 2'7 kilocycle control pulse frequently involved.

It can now be appreciated that when ythe tamper switch TS of anyapartment is closed, the presence of t3 pulses on the associateddoorbell line result-s in a control signal on the output 111 of thetamper switch signal circuit which signal is fed to an alarm bistablecircuit 122 to set the same which energizes the associated red light andprovides an alarm signal on the common alarm line 92 which energizesthehorn 98 and the Watch service telephone line (FIG. 1B).

When the key switch of the apartment involved is in a burglar alarmpreparing condition, the resulting presence of a t1 pulse on theassociated doorbell line 30 results in the generation on the output line124 of the key switch signal circuit 112 of a continuous gate openingsignal for the cycle yinvolved which signal is fed to one of the Vinputsof andAND alarm gate circuit 126 whose other input is coupled through adelay circuit 128 to the output 130 of the door switch signal circuit114, The output of the AND gate circuit 126 is fed to the alarm bistablecircuit 122. When two series of t2 pulses appear on the doorbell lineindicating two successive openings of a door or other monitored entrypoint involved, a control signal appears on the output line 130 of thedoor switch signal circuit 114 which is delayed in the circuit 128 foras much as 30 seconds to one minute before appearing at the input of thealarm gate 126. If the key switch is by that time returned to a burglaralarm turn-off position the AND gate circuit 126 will have closed due tothe termination of the aforesaid gate opening signal and the alarmbistable circuit 122 will not be triggered to its set alarm state.

The input of the supervisory signal circuit 116 is connected to aninverter circuit (not shown in FIG. 4) which provides an alarm controlsignal only in the absence of t4 control pulses on the doorbell line 30.Upon the absence of t4 control signals at time t4 on the doorbell line30, the supervisory circuit 116 generates a control signal on the output132 thereof which signal is fed to an .alarm bistable circuit 134 whichenergizes the associated White light 90-1 and generates an alarm signalon the common line 92 which sounds the horn 98 and energizes the watchservice telephone line.

` Although the drawings disclose only a burglar alarm system which isthe most important application of the invention, it should be understoodthat certain aspects of the invention are applicable to systems formonitoring temperature and other variables. For example, a lire alarmsystem can readily be super-imposed, on the circuit just described by,for example, placing a fusible lead or solder link 69 in each controlbox in series with each rectier 68-1 or 68-2 connected between the rearlisten line 36 used for supervisory purposes and the associated doorbellline. Thus, if a fire starts in the apartment, the line 69 will melt andthereby open the supervisory circuit `cuts-off the t4 pulses from thedoorbell line involved and initiates the various alarm operationsdescribed above. Any number of such links 69 could be positionedthroughout the apartment involved and connected in series circuitrelation in the supervisory circuit involved so that a number of pointsin the apartment could be monitored forre. Also, in a manner to beexplained, a garage calling system canV be readily incorporated with theburglar alarm of the present invention.

Other common lines (not shown) could also be used as a distributor ofpulses of other phases and additional v condition sensing switches could=be added between each such common line and individual control lines(such as doorbell lines) to Vprovide control signals having conditiondistinguishing phases to monitor various conditions in the sections ofthe building involved. The flexibility of the present invention is thusapparent.

It should also be appreciated that certain aspects of the presentinvention are applicable to office buildings,

and even individual homes as well as to apartment buildings.

A properly designed burglar alarm system should be tamper proof,employing protection means for the entire system. The protection meansis illustrated in FIGS. 5 and 6. As previously explained, the 'basementof the build-ing preferably contains the .alarm system cabinet orenclosure 50, which houses the alarm system and terminal board 17 andpower supply 26. The wires from and to the terminal board 17 are broughtout from enclosure 50 in conduit pipe 203, which extends to the variousrisers of the building. The AC power is brought into the alarm system onwires 209 and 210, which connect to the 6() cycle AC supply line of thebuilding. The wires 209, 210 and 53 are brought to the enclosure 50 froma remote location in a conduit 223. The watch service telephone line isalso at a remote location from the housing 50. A relay 211 havingnormally closed contacts 211-.1 is also located remotely with respect toenclosure 50. One terminal of the relay coil 211 is vconnected to ACline 210. The other terminal is connected to conductor 53 which wrapsaround enclosure 50 and is then brought into enclosure 50 connected atAC power wire 209. The conductor 53 extends spaced horizontal andvertical paths made possible by the rings 213 through which theconductor is threaded. Contact 211-1 has a terminal connected to watchservice telephone line ground, and another terminal connected to theWatch service telephone line. Conductor 53 and relay 211 taken togetherconstitute a power line supervision system. When conductor 53 is intact,the relay 211 is connected across power line wires 209 and 210, and isenergized which results in the opening of contacts. If wire 53 should becut for any reason, such as the unauthorized opening of the door 51 ofenclosure 50, then the relay will be de-energized. This results in theclosure of contact 211-1 which will signal the watch service over thetelephone line. If the AC power is removed from either wire 209 or 210,then relay 211 will become de-energized, resulting in an alarm signal tothe watch service, over the telephone line.

If someone tries to cut the pipe 203, and in so doing severs any of thedoorbell wires included within, then the supervision circuitrypreviously described will send out an alarm signal to the watch service.

EXEMPLARY LOGIC ANNUNCIATOR CIRCUIT OF FIGS. 7 AND l0 An individualapartment annunciator circuit 84-,1 whose block diagram is depicted inFIG. 4 is exemplified by the detailed logic diagram of FIG. 7. Alsoshown is the audible alarm and watch service circuit which is comprisedof bistable 94, horn 98, reset pushbutton switch 106, bistable 96, relay100, and pushbutton switch 108. Also shown is the logic power supply 78,and its various output terminals 77, 77 and 77 which provide voltages ofthe polarities shown with respect to logic ground L.

The key switch signal circuit 112 is comprised of bistable 212, and ANDgate 208. The door switch signal circuit comprises AND gate 214,integrating capacitor 215, resistor 213, level detector unit 216,counter 2.18 (which may be a single scale-of-two bistable pulsecounter), differentiating network 220, AND gate 219, and signal invertercircuit 249.

The tamper'switch signal circuit 110 is comprised of AND gate 232. Theburglar alarm output circuit 'is composed of OR gate 234, bistable 122,differentiating network 238, and alarm lamp 1.

The supervision signal circuit comprises signal inverter 240, and ANDgate 242. The supervision alarm circuit is composed of Vbistable 134,dilerentiating network 246, and supervision alarm lamp 90-1.

Each of the bistables (94, 96, 134, 2.12, 122 and 218) have two Iusableoutputs, and set and reset inputs. When a positive signal is applied toa set input, the output on that side (the set output) will become notpositive. The

reset side will become positive. Similarly, it a positive signal isapplied to a reset input, the reset output will become not positive, Theset side output will become positive. All AND gates have tWo inputs. AnyAND gate will deliver a positive voltage at its output only if both ofits inputs are positive. The OR gate 234 will .deliver a positivevoltage at its output if any of its inputs are positive. The time delaymeans 128 is illustrated in the form of a monostable multivibratorhaving two usable outputs, and one set input, resetting beingaccomplished internally. The counter bistable 218 has two states, andreverts to its original state on every second input signal fed thereto.

Consider the system when the key switch ICS-1 is in its burglar alarmturn-off position (door may be opened or closed), 'and the tamper switchTS-l open and bistables 122 and 134 are initially in their reset states.As described earlier, under these conditions, the doorbell line receivesno positive control pulses at times t1, t2 and t3. The doorbell lineconstitutes the input to signal inverter 240, and the first of inputconnections to AND gates 208, 214 and 232. Therefore, under the aboveassumptions, the AND gates 208, 214, and 232 are not in a condition tosupply positive voltage at their outputs.

At time to, a positive gating pulse will appear on gate line T0 which isconnected to the reset input of bistable 212 and the input to inverter249. The set input of bistable 212, which joins to the output of ANDgate 208, has no positive voltage on it; hence, bistable 212 will bereset, and remain so during all times, as long as the key switch is notin the alarm preparing position.

The inverter 249 as illustrated includes an NPN transistor 25'6 and`associated base circuit resistors 248 and 250, and collector resistor258. The emitter 254 of the transistor is connected directly to logicground L. The output from the inverter 249 extends from the collector260 to one of the inputs of AND gate 219 whose output is connected totheir set input of the counter bistable.

The positive potential (at this time to) on inverter circuit resistor248 causes a positive potential on base 252 of the transistor 256, dueto the potential divider effected by resistor 248 and resistor 250.Resistor 250 has one side connected to the negative power supplyterminal 77 and has its other side connected to base 252, to whichresistor 248 is also connected. Hence, transistor 256 is renderedconductive during time t0 and its collector 260, which constitutes oneinput to AND gate 219, is at logic ground potential. Therefore, theoutput of AND gate 219, which connects the reset input of counter 218,cannot supply positive voltage to reset the counter 218, at time t0.

For all times other than to, the lack of positive potential on theterminal of the base circuit resistor 248 allows the base 252 of thetransistor 256 to become negative with respect to emitter 254, causingtransistor f 256 to be non-conductive. The negative potential issupplied from power supply terminal 77 via resistor 250, to the base252. Hence, for times t1, t2, t3 and t4, a lpositive potential appearsat the output of inverter 249 which potential is obtained from powersupply terminal 77" which is connected to resistor 258 which terminatesat collector 160. Since bistable 212 remains reset when the key switchKS is not in the alarm preparing position, its set output, whichconnects to the second input of AND gate 219 will be positive. Thus, ANDgate 219 has both inputs positive, which applies a positive voltage fromits output to `the `reset input of the counter 218, causing the counterto reset to its normal state.

Assume that the key switch KS, is now turned to the alarm preparingposition by the tenant. At time t1 a positive gating pulse will appearon the gate line T1' of AND gate 208 which constitutes the second inputto AND gate 208. The other input thereof will also have a positivecontrol pulse present at this time. A positive voltage will then appearat the output of AND gate 208 which will appear on the set input ofbistable 212, rendering its set output not positive. At time to,bistable 212 will again be reset, but at time t1 will again be set, andremain set until the l0 gating pulse again occurs. Hence, during timest1, t2, t3 and t4, when the key switch is turned to the alarm preparingposition, the input to AND gate 219 connected to the set output ofbistable 212 is not positive. At time t0, as explained above, the inputto AND" gate 219 from transistor 256 is not positive. Therefore, at notime are both inputs to AND gate 219 positive under the conditions nowbeing described. And no reset signal will be applied to the counter 218reset input.

Now, suppose the tenant leaves his apartment for the first time. Whilethe door is open, positive control pulses will be fed into the firstinput of AND gate 214, at each time t2. At time t2, a positive gatingpulse is led into the second input of AND gate 214. A series of positivevoltage pulses results at the output of AND gate 214 0ccurring at eachtime t2. The output pulses of AND gate 214 will be collected uponintegrating capacitor 215 via its connection to resistor 213, connectedto the output of gate 214. The ungrounded side of capacitor 215 isconnected to the set input of normally reset monostable circuit 216. Thevoltage will build up on capacitor 215; when it reaches a sufficientpotential above logic ground, the monostable multivibrator leveldetector circuit 216 Will be set through its set input connected to thecapacitor 215 and` will remain set until the voltage on capacitor 215discharges below a circuit setting value. A sudden positive going outputof the level detector 216 caused by the setting thereof is fed to thepulse input 217 of the counter 218 where it is differentiated, theresulting positive pulse being directed to the set input of the counter.The counter 218 now changes state, indicating that the door in theapartment has been opened for the first time. The level detector 218-rernains switched until the door is closed, at which time the voltageon capacitor 215 decays, because no more pulses emanate from the outputof gate 214, since its first input is no longer fed positive controlpulses from the doorbell line at time t2.

Assume that the tenant returns home. When the door is opened for thesecond time, the level detector monostable 216 will again be set asdescribed above. The change in its output will be applied to the pulseinput 217 of the counter 218, where it is differentiated and fed as apositive pulse to the reset input of the counter 218. The counter nowtransmits to its original reset state. During this transmission, the setoutput of the counter 218 is positive going, and will be fed throughdifferentiating network 220 to the set input of the time delay circuit128 as a positive pulse. The time delay circuit is a monostablemultivibrator which in the act of returning to its reset state aftermany seconds (like 30-40 seconds later) feeds a positive going pulse tothe differentiating network 230. This time delay is of sufficientduration to allow the tenant to remove the key switch from its alarmpreparing position. When the tenant does so, bistable 212 will be reset,as previously described. Upon termination of the time delay the positivegoing output of the monostable 128 is fed through differentiatingnetwork 230, is converted to a positive pulse fed to the first input ofthe alarm AND gate 126, the second input of the alarm AND gate 126 isconnected to the reset output of bistable 212 in the key switch signalcircuit which is now not positive, since the system is not in the alarmpreparing condition. Hence, alarm gate 126 will block the positive pulseoriginating from the delay circuit 128.

Assume that a burglar enters the apartment. The burglar will not be ableto remove the key switch from the alarm preparing condition, in suicienttime. Hence, bistable 212 will remain in its set condition (its resetoutput being at positive potential). This time, upon termination of thetime delay, the positive pulse from the delay monostable |28 at thefirst input of' the alarm gate 126 will cause a positive pulse at theoutput of alarm AND gate 126, since the second input to the alarm gateis now positive also. The output of alarm gate 126 feeds the positivesignal to the rst input of OR gate 234 which feeds a positive pulse tothe set input of bistable 122. The reset output of bistable 122 is thena positive going voltage which is passed through differentiating network238 as a positive pulse to the common alarm line 92. The set inputs ofthe bistables 94 and 96 are connected to this line. Hence, both of thesebistables are set, causing the horn 98, which is connected between theset side of bistable 94, and the power supply terminal 77" to sound. Thereset side of bistable 96 goes from ground to positive potential. Thiswill cause the normally energized relay 100, which is connected betweenthe reset output of bistable 96 and power supply terminal 77" to becomedeenergized. The relay contact 102 will then connect the watch servicetelephone line to the telephone system grounds T. This will summon thewatch service patrolman to the building being burglarized. Alarm lamp90-1, which is connected between the reset output of bistable 122 andthe power supply terminal 77 will be energized, giving a visualindication of the exact apartment being burglarized.

When indication of a burglary is no longer required, the resetpushbutton switches, all of which have one side connected to powersupply terminal 77" may be depressed.

When the pushbutton switch 106 is depressed, it will apply positivepotential to the reset input of bistable 94. This will cause the horn tobe silenced. When pushbutton switch 108 is depressed, it will apply apositive potential to the reset input of bistable 96. This will causerelay 100 to become energized, thus removing the telephone line from thetelephone ground T.

When the lamp reset pushbutton switch 104 is depressed it will apply apositive potential on a common reset line S, which is connected to thereset inputs of bistables 122 and 134. Bistable 122 will return to itsreset state, and the alarm lamp 90-1 will be extinguished.

Suppose that upon entering the apartment the burglar immediately triesto disable the alarm system by removing the control box panel from thewall of the apartment. Upon doing so the tamper switch TS-1 will close.At time t3, which will occur within a fraction of a second, a positivecontrol pulse will appear on doorbell line 30-1" which is connected tothe first input of AND gate 232. At this time the second input of ANDgate 232, which connects to gate line T3 will also receive a positivepulse. This will result in a positive pulse at the output of AND gate232, which will be fed into the second input of OR gate 234. Bistable122 is then triggered as before. This results in energization of alarmlamp 90-1, the horn 98 and a grounding of the telephone line, just asbefore. In this instance, however, the alarm conditions were introducedwithout any time delays.

The supervision feature of the system will determine and indicatewhether or not the associated doorbell line has been severed. When thedoorbell line is intact, a positive control pulse will appear on thedoorbell line 30-1 at time t4. This pulse is fed into the input ofsignal inverter 240 which is like inverter 249 previously described. Theoutput of inverter 240 then produces ground potential, which will appearat the rst input of AND gate 242. The output of AND gate 242, whichconnects to the set input of bistable 134, will not produce a positivepulse. Hence, bistable 134 will remain reset. Assume that the doorbellline is cut. At time t4 no signal will appear at the input of inverter240, and its output will appear as a positive potential at the iirstinput of AND gate 242. At time t4, a positive gating signal appears ongate line T4' which connects the `second input of AND gate 242. Theresulting positive output of AND gate 242, will set bistable 134. Thepotential at the reset output of bistable 134 will transfer fromnegative polarity to ground. This positive voltage transition will befed through 18 differentiating network 246, onto the common alarm line92 as a positive pulse. The bistables 94 and 96 will be set as describedearlier. The supervision lamp -1 which is connected between the resetoutput of bistable 134 and the power supply terminal 77 will light up,thereby indicating that the doorbell wire has been cut.

The door switch signal circuit 114 which is depicted in FIG. 7 bysymbolic elements 214, 215, 216, 218, 220, 219, and 249, is detailed inFIG. 10, where like elements have been given like reference.

When the key switch of the associated apartment is in the alarmpreparing position, positive control pulses will be for through arectifier 280 to one side of a resistor 281 from the associated doorbellline at time t1. However, the output of AND gate 214, which is 4at thejunction of the anode of rectifier 283 and the other side of resistor281, will not be positive during time t1 since the gate line T2' whichconnects to the cathode of the rectitier 283 is not positive at thistime. If the associated door is not open at time t2, no positive controlpulse will be on the associated doorbell line 30-1" at that time and theoutput of AND gate 214 will not be positive even when a positive pulseappears at time t2 on the gate line T2'; this pulse is blocked byrectifier 283. However, when the monitored door of the apartment isopened at any time t2, a positive control pulse will be fed to theresistor 281 which is the rst input to AND gate 214, at the same time at2 pulse is fed to the second input to the AND gate 214 at the input torectiiier 283. The output of AND gate 214 will then be a positivepotential. A negative or ground potential at the anode of rectier 283 attimes other than t2 would pass through the rectilier to make the outputof the AND gate at this negative or ground potential. Thus, both inputsto AND gate 214 must be positive to provide a positive potential at itsoutput. At a pulse repetition rate of 20,000 pulses per second a largenumber of pulses will appear -at the output of AND gate 214 even whenthe door is momentarily opened. This series of pulses will pass throughdiode 282 and charge the integrating capacitor 215 to a positivepotential with respect to logic ground.

The level detector monostable circuit 216 has a PNP transistor 292 whichis conducting when the level detect-or 216 is in its normal reset statebecause it is forwardly biased from the negative potential of powersupply terminal 77, which is fed to base 291 through resistor 284. Whentransistor 292 is conducting, a PNP transistor 294 forming part of themonostable circuit wil be nonconductive due to the positive potentialfed to its base from the power supply terminal 77".

When the voltage in capacitor 215 becomes sulciently positive it willback bias the base to emitter junction of transistor 292 and cause it tocease conduction. This increases the negative voltage on the collectorof transistor 292 which causes transistor 294 to start conducting due tothe more negative voltage connected to its base through resistors 290and 286.

To insure that transistor 292 becomes and stays nonconductive until thepositive pulses from AND gate 214 cease, transistor 294 institutes .apositive feedback potential as it becomes conductive, which is appliedto the base 291. This signal is applied via capacitor 288 connectedbetween the collector of transistor 294 and the base 291 of transistor292 and renders base 291 more positive until capacitor 215 has `beenable to more fully charge positively. This positive feedback potentialwill finally decay as capacitor 288 discharges through resistor 284; thedecay time being greater than the period between the positive pulsesfeeding through diode 282. Thus, the transistor 292 is renderedcompletely non-conductive, and the transistor 294 fully conductive. Thelevel detector 216 is now in its set state, and remains so Ias long aspositive pulses continue on the doorbell line involved at time t2 (whenthese pulses cease, the capacitor 21S discharges and recharges to anegative voltage which returns transistor 292 to a conductive stateforcing transistor 294 to a nonconductive state).

At the inception of the set state, the voltage on the collector oftransistor 294 is positive going, since a change from negative to groundpotential occurs.

As transistor 294 becomes conductive in the set state of the leveldetector, the voltage on its collector is applied to the pulse inputterminal 217 of the binary counter 218 by a conductor 275. The counteris a scale of two counters composed of PNP transistors 296 and 298 whichare cross coupled to form a bistable circuit having the control inputsthereofv fed from input terminals 217 through capacitors 295 and 297,and diodes 293 and 299. Each time the level detector is triggered intoits set state by the opening of the associated apartment door, thetransistors 296 and 298 will lreverse states of conduction, one beingconductive and the other non-conductive.

t If the associated key switch KS is in its alarm preparing positions,the associated ldoor is opened by the tenant as he leaves the apartment,transistor 296 becomes non-conductive. The network 220, comprisingresistor 289, and capacitor 285, which is connected to the collector oftransistor 296, develops a negative pulse which is blocked by diode 287.

When the door is opened for the second time, transistor 296 will go intoconduction. The positive change in potential at the collector of thistransistor will be relayed as a positive pulse to line 300, via thedifferentiating network 220, thereby initiating the time delay.

Signal inverter 249 has previously lbeen described in detail inconjunction with FIG. 7. A positive to pulse fed to the inverter-resistor 248 from gate line T will force inverter transistor 256 intoconduction, applying ground potential at its collector 260. At othertimes, the voltage on terminal T 0 is at ground potential yand collector260 will be positive only if the set output of bistable 212 of the keyswitch signal circuit (FIG. 7) is positive. This output will be positivewhen the key switch is in its burglar alarm turn-off position. At thistime transistor 298 of the counter 218 is turned off due to the positivepotential fed to its base from the power supply terminal 77 throughresistors 258 and 279. The counter is now in its reset state, indicatingthat the associated door has not been opened at all. When the key switchKS is turned on, the set output of the bistable 212 of the key switchsignal circuit goes to ground potential, thereby holding collector 260at ground potential through diode 277. The counter is now free to leaveits normal state, upon receipt of the proper signal at its pulse input217.

GARAGE CALL CIRCUIT (FIGS. 8 AND 9) An additional feature that canreadily be added to the existing burglar alarm system is a garagecalling system. With this system the tenant may signal the garage, whenthe key switch KS is not in the -alarm preparing position, indicatingthat he will shortly be coming there for his car.

An additional signalling line of the building, the rear talk line 35 canbe utilized for transmitting positive control pulses at time t which isnot in phase with times t0, t1, t2, t3, and t4, to all the apartments.The control pulse at time phase t5 can be generated lby merely adding asixth position to the ring counter 73 and an output line 72-5 (see FIG.9) which feeds the base of transistor 75-5, and causes said transistor,the emitter of which is connected to positive power supply terminal 77',to apply a positive control pulse at the pulse generating terminal T5 attime t5. The pulse gene-rating terminal T5 is connected to the rear talkline 35.

When the rear talk line is utilized, an additional isolating powersupply 63 having a voltage output greater than the magnitude of the t5control pulses is required, and is connected at its negative terminal tothe rear listen line 36, and at its positive terminal to the rear talkline 35 to which is also connected the negative terminal of :enogaasisolating power supply 63', which has been moved from its previousconnection on line 36. The isolating power supply 63 will prevent afeed-through of the t5 control pulse, from the rear talk line 35 to therear listen line 36 vi-a the mutual impedance between them.

To further implement the garage calling system a garage callswitch 260is added to the apartment control box 18, and is connected at its firstterminal to branch line 35-1 or 35-2, etc. which connects to the reartalk line 35, and atl its second terminal to the anode of isolatingrectifier 262, the cathode thereof connecting the associated doorbellline 30 (see FIG. 8). When the garage call pushbutton switch 260 isdepressed, a positive control pulse wil be coupled from rear talk line35 to the associated doorbell line.

Additional logic circuitry like that depicted in FIG. 9 must beintroduced, the purpose of which is to respond to the presence of t5control pulses. This additional circuitry is exemplified by the logicdiagram of FIG. 9. The garage call logic circuitry 0f each apartment iscomprised of AND gate 264 and bistable 266 and OR gate 265. Located inthe garage is display panel 270, which houses lamps 271. Also in thegarage is a reset pushbutton switch 269 which is connected betweencommon reset line 267 and logic power supply terminal 77". The commonreset line is connected to the first input terminal of all OR gate 265.The secon'd input of OR gate 265 is connected to the reset output ofbistable 212. The rst input of AND gate 264 is connected to theassociated doorbell line; the second input thereof is connected to agate line T5 which is connected to the output of a gate circuit 82-5which acts like the aforesaid AND gates 82-0 etc. The reset output ofbistable 266 is connected to one of the terminals of the associatedsignal lamp 271, which is housed in annunciator display panel 270. Theother terminal of each lamp 271 is connected to power supply terminal77. Line 272 connects the other signal lamps with the associated garagecall logic circuitry of the other apartments.

If the key switch KS of the apartment involved, is in its alarmpreparing condition, the reset output of bistable 212 will be positiveand will thus apply a positive signal to the reset input of bistable 266at all times other than to, thereby holding its reset output reset atnegative potential irrespective of the signals appearing at its setinput. At time l5, if the key switch KS of an apartment is closed, t5control pulses will feed through isolating power supplies 63", 63', andthe test power supply 63 onto the lirst listen line 32 and to theassociated doorbell line via isolating rectifier 56. This will applypositive pulses at the rst input of AND gate 264 at time l5, even thoughthe garage call switch 260 has not been depressed. However, the resetoutput of bistable 266 will still remain reset because of the positivesignal applied to its reset input, as described above.

When the key switch KS is not in its alarm preparing condition, and thegarage call pushbutton switch 260 is not activated, no control pulsewill appear on the associated doorbell line at time t5, and the firstinput of AND gate 264 will not be positive, resulting in no output.

If the occupant of an apartment now depresses garage call switch 260,positive control pulses will appear at the first input of AND gate 264at time t5 simultaneously with the feeding of t5 gating pulses to thesecond input of AND gate 264. Therefore, the output of AND gate 264 willfeed a positive pulse into the set input of bistable 266, at time t5,which will set bistable 266. The reset output of bistable 266 is now atground potential, and will energize the associated lamp 271, whichindicates to the garage attendant, that the occupant of the apartmentinvolved wants his car. After the garage attendant has obtained thetenants car he can extinguish lamp 271 by depressing reset pushbuttonswitch 269. This will apply a positive potential at the rst input of ORgate 265 which results in a positive signal on the reset input ofbistable 266, causing the reset output to go negative, which results inturning oit lamp 271.

It should be understood that numerous variations may be made in theforms of the invention described above without -deviating from thebroader aspects thereof.

We claim:

1. In a building or the like including a number of sections having afirst common line extending therebetween and forming part of a rstcommon circuit, a second common line extending between said buildingsections and forming part of a second common circuit and an individualline extending to each section of the building and completing anindividual circuit associated with the building section, and powersupply means for providing energizing power on said common andindividual lines for said circuits, the improvement comprising amonitoring system superimposed on said common and individual lines "formonitoring a given condition in each section of the building comprising:a separate condition sensing switch means for each section of thebuilding operated to an alarm condition when the condition to bemonitored is present in the associated building section; a preparingswitch means for each section of the building having an alarm preparingand an alarm disabling condition; control signal generating means forapplying a rst control signal having a rst distinguishing characteristicto said irst common line and a second control signal having a seconddistinguishing characteristic to said second common line; means couplingeach of said separate condition sensing switch means between said firstcommon line and the individual line extending to the associated buildingsection for providing on the individual line involved said :firstcontrol signal only when the associated condition sensing switch meansis in its alarm condition; means coupling each preparing switch meansbetween said second common line and the individual line extending to theassociated building section for providing on the individual lineinvolved said second control signal only when the preparing switch meansis in its alarm preparing condition; and control signal responsiveannunciator means responsive only to the combined presence of said firstand second control signals on any of said individual lines forsignalling an alarm for the section of the building involved.

2. The monitoring system of claim 1 wherein said first and secondcontrol signals are respectively pulses of the same pulse repetitionrate but different phase, and there is further provided means forpreventing interaction between said energizing power and said controlsignals respectively on the annunciator means and the signallingcircuits, said interaction preventing means comprising means forcyclically disconnecting said power supply means from said lines forlimited time intervals during which the monitoring system is operable,and means for inhibiting operation of said monitoring system during theintervening time intervals.

3. In an electrical system including a iirst, second and third lineforming part of an electrical system; and power supply means providingenergizing power on said lines for said electrical system; theimprovement comprising an annunciator system superimposed on saidelectrical system for determining when a first and/or a second speciedcondition occurs comprising: (a) a first condition alerting switch meansoperated to a notifying condition when said rst specified conditionoccurs; (b) a second condition alerting switch means operated to anotifying condition when said second speciiied condition occurs; (c)means for respectively cyclically coupling rst and second control pulsesto said rst and second respective lines which pulses respectively have arst and a second predetermined phase, at least one first and one secondcontrol pulse occurring in each cycle of said rst and second controlpulses; (d) means coupling said first condition alerting switch meansbetween said irst line and the third line for providing on the thirdline involved said first control pulses only when the associated firstcondition alerting switch means is in its notifying condition; (e) meanscoupling said separate second condition alerting switch means betweensaid second line and the third line for providing on the third lineinvolved said second control pulses only when the second conditionalerting switch means is in its notifying condition; (f) annunciatormeans responsive to said first and second control pulses on said thirdline; (g) and means for preventing interaction of said electrical systemon said annunciator system, said interaction preventing means comprisingcontinuously operating Iautomatic switching means for cyclicallydisconnecting said power supply means from said lines for limited timeintervals during which the annunciator system is operable, saidannunciator system being inoperative during the intervening timeintervals, and the electrical system being non-responsive to saidcontrol signals during said intervening time intervals.

4. The combination of claim 3 wherein the pulse repetition rate of saidcontrol pulses are at least as high as the frequency of disconnection ofsaid power supply means.

5. The combination of claim 3 wherein said electrical system includesmomentarily operable manual switch means for momentarily connecting saidpower supply means to at least one of said lines at the will of theoperator, and the switching rate of said automatic switching means beingsuiciently high that at least one cycle of operation thereof will alwaysoccur during the momentary operation of said manual switch means.

6. The combination of claim 3 wherein said electrical system includes anaudible communication system, and said control pulses being at anon-audible pulse repetition rate.

7. A burglar alarm system for a building having individual apartments orsections each with a door leading thereto, said burglar alarm systemcomprising: a door switch opposite each door which switch has a firstcondition when the door is closed and a second condition when the dooris opened; a manually operable prepare means for each apartment orsection of the building for preparing the alarm system for operationthereat when operated to a given condition; signal counting means foreach section of the building for providing an alarm operating signal foreach two control signals fed thereto; means associated with each doorswitch and responsive each time the associated door switch is operatedfrom said iirst to said second condition for feeding a control signal tothe signal counting means of the associated section of the buildingprovided the prepare means is in said given condition; and annunciatormeans for each section of the building responsive to the alarm operatingsignal 'of the associated signal counting means for signalling an. alarmfor such section of the building.

8. The burglar -alarm system of claim 7 wherein each building sectionhas additional points of entry to be monitored other than said door, anentry switch like said door switch at each entry point which has iirstand second conditions like said door switch when the entry points arerespectively closed and opened and said entry switches being connectedin parallel with said door switch wherein said door switch responsivemeans responds in the same way to successive openings of any point ofentry to the apartment.

9. A burglar alarm system for a building having at least one point ofentry, said burglar alarm system comprising: an entry sensing means atsaid entry point having an alarm condition when the entry point iscrossed; a manually operable prepare means for said point of entry forpreparing the alarm system for operation independently of the conditionof said entry sensing means when operated to a given prepare condition;signal counting means for providing an alarm operating signal for eachtwo control signals fed thereto; means responsive each time any entrysensing means is operated to said alarm condition and said prepare meansis in said prepare condition by feeding a control signal to the signalcounting means; and annunciator means responsive to the alarm operatingsignal of the signalcounting means for signalling an alarm condition forthe building.

10. The burglar alarm system of claim 9 wherein said annunciator meansincludes means preventing the signalling of said alarm unless saidprepare means is an remains in said prepare condition for a period inexcess of the time required-for an occupant passing said entry point tooperate the prepare means to said prepare condition.

11. A burglar alarm system vfor monitoring the unauthorized entry of aperson through an entry point thereof, said burglar alarm systemcomprising: entry sensing switch means opposite said entry point whichswitch means has a first normal condition and a second condition when aperson passes said entry point; an alarm preparing switch operable to arst burglar alarm preparing condition and a second burglar alarmturn-off condition; an audible device; and means responsive to thesimultaneous operation of an entry sensing means to said secondcondition and the associated alarm preparing switch to its burglar alarmpreparing condition for operating the associated audible device duringevery passage of the entry point, wherein a person is automaticallyalerted to the operating condition of the burglar alarm as he passessaid entry point while entering or leaving the same; means responsive tosaid second condition of the entry sensing means every second time theentry point is passed and the burglar alarm preparing condition of thealarm preparing switch for signalning an alarm for the section of thebuilding involved after a delay period suflicient to enable a p'ersonmaking lawful entry to operate said alarm preparing switch to saidburglar alarm turn-off condition, if the switch is not so operated saidalarm being independent and distinguishable from the audible alarm ofsaid audible device.

12, In a building 0r the like having individual sections each having anentrance door with a key operated lock which can be picked by an expertlock picker in a given time; at least two Common lines extending betweenthe apartments; individual lines extending respectively to the differentsections of the building, a burglar alarm system, said burglar alarmsystem comprising:

(a) a door switch at each building section entrance door which has a rstcondition when the door is closed and a second condition when the dooris opened;

(b) an alarm preparing key switch within each building section, the keyswitch including a key operated lock which requires a much greaterpicking time than said given time and operable by insertion of a key inthe associated lock to a rst burglar alarm preparing condition or asecond burglar alarm turn-off condition',

(c) means for respectively cyclically coupling control pulses to saidcommon lines respectively having a first and a second predeterminedphase;

(d) means connecting said alarm preparing means in each building sectionbetween one of said common lines and the individual line extending tothe building section involved for coupling control pulses of said firstpredetermined phase to the associated individual line only when theassociated alarm preparing switch is in said alarm preparing condition;

(e) means for connecting said door switch of each building sectionbetween the other of said common lines and the individual line extendingto the associated building section involved for coupling control pulsesof said second predetermined phase to the associated individual lineonly when the associated door switch is operated to said secondcondition by the opening of the associated door;

(f) and annunciator means responsive to only the combined presence ofthe control pulses of said first and second predetermined phase on anyof said individual lines by signalling an alarm for the building sectioninvolved, if such pulses persist after a predetermined delay intervalgreater than said given period which enables a building occupantre-entering his section to operate the associated alarm preparingswitchto a burglar alarm turn-off condition.

13. In a building -having different sections with an entrance doorclosing off each section, a rst commonline extending between the varioussections of the building, and individual control lines extending to thevarious sections of the building, a burglar alarm system comprising: (a)a door switch opposite each said entrance door which door switch has afirst conditionwhen the door is closed and a secondA condition when thedoor is opened; (b) means for cyclically applying control pulses of afirst predetermined phase to said first common line; (c) meansconnecting the door switch is each section of the building between saidfirst common line and the individual control line extending to thesection of the building involved for coupling control pulses of saidfirst phase to the indvidual control line only when the associated doorswitch is operated to said second condition by the opening of theassociated door; (d) adoor switch responsive circuit for each buildingsection and having a first input connected to the associated individualcontrol line and a second input, means connecting control pulses havingsaid first phase to the second inputs of all the alarm preparing switchresponsive circuits, gate means for providing a control signal each timethere is coincidence between the pulses at said first and second inputsof the door switch responsive circuit, pulse integrating meansselectively responsive only to closely following repetitive controlpulses provided by said gate means resulting from each door opening byproducing a voltage which rises to a given threshold level, a firstscale of two counter bistable circuit responsive to said voltage outputof said pulse integrating means by changing from one state to anothereach time said voltage output rises to said threshold level, wherein thelatter bistable circuit is triggered into a set state every two timesthe door 0f the associated apartment is opened; and (e) means responsiveto the set state of said first bistable circuit by signalling an alarmfor the building section involved.

14. In a building having different sections with an entrance doorclosing off each section, a first and a second comon line extendingbetween the various sections of the building, and individual controllines extending to the various sections of the building, a burglar alarmsystem comprising: (a) a door switch opposite each said entrance doorwhich door switch has a rst condition when the door is closed and asecond condition when the door is opened; (b) an alarm preparing switchfor each section of the building operable to a burglar alarm settingcondition and a burglar alarm turn-off condition; (c) means forcyclically applying control pulses of a first predetermined phase tosaid first common line and of a second predetermined phase to saidsecond common line; (d) means connecting the door switch in each sectionof the building between said first common line and the individualcontrol line extending to the section of the building involved forcoupling control pulses of said first phase to the individual controlline only when the associated door switch is operated to said secondcondition by the opening of the associated door; (e) means connectingthe alarm preparing switch in each section of the building between saidsecond common line and the associated individual control line eX-tending to the section of the building for coupling control pulses ofsaid second phase to the control line involved only when the associatedalarm preparing switch is in said alarm setting condition; (f) a doorswitch responsive circuit for each building section and having a rstinput connected to the associated individual control line and a secondinput, means feeding control pulses having said first phase to thesecond inputs of all the alarm preparing switch responsive circuits,gate means in each door switch responsive circuit for providing acontrol signal each time there is coincidence between the pulses at saidfirst and second inputs of the door switch responsive circuit, pulseintegrating means selectively responsive only to closely followingrepetitive control pulses provided by said gate means resulting fromeach door opening by producing a voltage which rises to a giventhreshold level, a first scale of two counter bistable circuitresponsive to said voltage output of said pulse integrating means bychanging from one state to another each time said voltage output risesto said threshold level, wherein the latter bisable circuit is triggeredinto a set state every two times the door of the associated apartment isopened; (g) an alarm preparing switch responsive circuit for eachapartment section of the building having a rst input connected to theassociated individual control line and a second input, means connectingcontrol pulses having said second phase to all the second inputs of saidalarm preparing switch responsive circuits, and a second bistablecircuit operated in a stable reset state when there is no coincidencebetween the control pulses at said iirst and second signal inputsthereof and operated in a stable set state when there is coincidencebetween said control pulses at said rst and second signal inputs thereo;(h) and means responsive to the coinciding of the set state of saidiirst and second bistable circuits of the associated alarm preparing anddoor switch responsive circuits by signalling an alarm for the buildingsection involved provided the second bistable circuit is not resetduring a predetermined delay interval permitting an occupant of abuilding section entering the same to operate said alarm preparingswitch to said burglar alarm turn-oit condition.

15. In an apartment building including: (l) an entrance hall withindividual manually operable apartment doorbell switches, a transmitterunit and a receiver unit, an entrance hall door on an inside wall ofsaid entrance hall blocking the entrance into the building from thehallway; (2) individual apartments each having an entrance door blockingentry to the apartments each having an entrance door blocking entry tothe apartment, a transmitter and a receiver unit, and a doorbell; (3)common power supply means; (4) a common listen line connected with saidpower supply means, all the apartments receiver units and the hallwaytransmitter units for enabling the apartment occupants to hear a visitorspeaking into the hallway transmitter unit; (5) a common talk lineconnected with said power supply means, all the apartment transmitterunits and the hallway receiver unit for enabling lthe apartmentoccupants to talk to a visitor listening to the hallway receiver unit;(6) and individual doorbell lines each connected with said power supplymeans, a different apartment doorbell and a diierent hallway doorbellswitch for energizing the associated doorbell when the associatedhallway doorbell switch is operated; the improvement in a burglar alarmsystem comprising:

(a) a door switch at each apartment entrance door which has a irstcondition when the front door is closed and a second condition when thefront door is opened;

(b) an alarm preparing switch in each apartment operable to ta iirstburglar alarm preparing condition and a second burglar alarm turn-ottcondition;

(c) means for respectively cyclically coupling to said common linescontrol pulses having a rst and second phase;

(d) means connecting the alarm preparing switch in each apartmentbetween one of said common lines and the associated doorbell line forcoupling pulses of a rst predetermined phase to the associated doorbellline only when the associated alarm preparing switch is in said alarmpreparing condition;

(e) means connecting said door switch of each apartment between anotherof said common lines and the associated doorbell line for couplingpulses of a second predetermined phase to the associated doorbell lineonly when the door switch is operated to said second condition by theopening of the associ-ated door;

(f) and an annunciator means responsive only to the combined presence ofpulses of said iirst and second predetermined phase on any of saiddoorbell lines for signalling an alarm for the apartment if such pulsespersist after a predetermined delay which enables an apartment occupantre-entering his own apartment to operate said alarm preparing switch andmeans.

16. In an apartment building including: (l) an entrance hall withindividual manually operable apartment doorbell switches, a transmitterunit and a receiver unit, an entrance hall door on an inside wall ofsaid entrance hall blocking the entrance into the building from thehallway, and a solenoid operated lock for the door which enables thedoor to be opened when energized; (2) individual apartments each havingan entrance door blocking entry to the apartment, a transmitter and areceiver unit, a doorbell, and a manually operable solenoid operatingswitch; (3) common power supply means; (4) a common solenoid lineconnected with said power supply means, all the apartment solenoidoperating switches and said solenoid operated lock for electingenergization of the solenoid operable lock when a solenoid operatingswitch in any apartment is operated; (5) a common listen line connectedwith said power supply means, all the apartments receiver units and thehallway transmitter units for enabling the apartment occupants to hear avisitor speaking into the hallway transmitter unit; (6) a common talkline connected with said power supply means, all the apartmenttransmitter units and the hallway receiver unit for enabling theapartment occupants to talk to a visitor listening to the hallwayreceiver unit; (7) and individual doorbell lines each connected withsaid power supply means, a different apartment doorbell and -a differenthallway doorbell switch for energizing the associated doorbell when theassociated hallway doorbell switch is operated; the improvement in aburglar alarm system comprising:

(a) a door switch at each apartment entrance door which has a rstcondition when the front door is closed and a second condition when thefront door is opened;

(b) an alarm control box in each apartment, the box having a removablepanel thereon;

(c) an alarm preparing key switch exposed for the outside of each alarmcontrol box in each apartment and operable by the insertion thereto andmovement of a key to a first burglar alarm preparing condition and asecond burglar alarm turn-oli condition;

(d) a tamper switch in each alarm control box which has an alarmcondition when the removable panel is moved to an alarm box openingcondition and an inoperative condition when the panel is an alarm boxclosing condition;

(e) means for respectively cyclically coupling to said common linescontrol pulses having a first, and a second, and a third phase;

(f) means connecting the alarm preparing key switch in each apartmentbetween one of said common lines and the associated doorbell line forcoupling pulses of a tirst predetermined phase to the associateddoorbell line only when the associated alarm preparing switch is in saidalarm preparing condition;

(g) means connecting said door switch of each apartment between anotherof said common lines and the associated doorbell line for couplingpulses of a second predetermined phase to the associated doorbell lineonly when the door switch is operated to said second condition by theopening of the associated door;

(h) means connecting said tamper switch in each apartment between stillanother of said common lines and the associated doorbell line forcoupling pulses of a third predetermined phase to the associateddoorbell line when the tamper switch is operated to its alarm condition;

(i) an annunciator means responsive only to the corn- -bined presence ofpulses of said first and second predetermined phase on any of saiddoorbell lines for signalling an alarm for the apartment if such pulsespersist after a predetermined delay which enables an apartment occupantre-entering his own apartment to operate said alarm preparing key switchand means;

(j) and annunciator means responsive only to the combined presence ofpulses of said first and third predetermined phase on any of saiddoorbell lines for immediately signalling an alarm for that apartment.

17. In a building or the like including a number of sections having afirst and second common line extending ybetween the various sections ofthe building, and an individual control line extending to each sectionfor monitoring a given condition in each section of the buildingcomprising: a condition sensing switch means for each section of thebuilding operated to an alarm condition when the condition to `bemonitored is present in the associated building section; control signalgenerating means for cyclically applying control pulses of a first phaseto said first common line and control pulses of a second phase to saidsecond common line; means coupling each said said condition sensingmeans between said first common line and the individual control lineextending to the associated building section for providing on theindividual control line involved control pulses of said first phase onlywhen the associated condition sensing switch means is in its alarmcondition; means continuously connecting the pulses on said secondco-mmon line to all of the individual control lines extending to thevarious sections of the building; and pulse responsiveannunciator meansfor each section of the building responsive to the presence of controlpulses of said first phase on the associated individual control line forsignalling a first alarm for the associated section of the buildingindicating the presence of the monitored condition and responsive to theabsence of control pulses of said second phase on the associatedindividual control line -for signalling a second alarm for theassociated section of the lbuilding indicating a defect in the alarmsystem.

18. A burglar alarm system for monitoring the unauthorized entry `of aperson through an entry point thereof, said burglar alarm systemcomprising: entry sensing switch means opposite said entry point whichswitch means has a rst normal condition and a second condition when aperson passes said entry point; an alarm preparing switch operable tofirst burglar alarm preparing condition and a second burglar alarmturn-off condition;

an audible device; and means responsive to the simultaneous operation ofan entry sensing means to said second condition and the associated alarmpreparing switch to its yburglar alarm preparing condition for operatingthe associated audible device only during the passage of the entrypoint, wherein a person is automatically alerted to the operatingcondition of the burglar alarm as he passes said entry point; a manualreset switch; means responsive to said second condition of the entrysensing means every second time the entry point is passed and theburglar alarm preparing condition of the alarm preparing switch forsignalling an alarm for the section of the building involved after adelay period sufiicient to enable a person making lawful entry tooperate said alarm preparing switch to said burglar alarm turn-offcondition, if the switch is not so operated, said alarm beingindependent and distinguishable from the audible alarm of said audibledevice, said alarm persisting until said reset switch is operated.

19. In an apartment building or the like including an entrance hall withindividual manually operable apartment -ringing switches; individualapartments each having an entrance door with a key operated lock whichcan be picked by an expert lock picker in a given time and ringing meansto be operated by one of said manually operable switches in the entrancehall; a signalling system 'between said apartments and the entrance hallincluding at least two common lines extending between the apartments andthe entrance hall area; individual control lines completing apartmentringing circuits extending between the manually operable switches in theentrance hall and said ringing means in the individual apartments; andpower supply means coupled to said common lines and said individualcontrol lines for energizing said signalling system and ringingcircuits; a burglar alarm system superimposed `on said signallingsys-tem and the ringing circuits, said burglar alarm system comprising:

(a) a door switch at each apartment entrancedoor which has a firstcondition when the door is closed and a second condition when the dooris opened;

(b) an alarm preparing key switch within each apartment, the key switchincluding a key operated lock which requires a much greater picking timethan said given period of time and operable by insertion of a key in theassociated lock to a first burglar alarm preparing condition or a secondburglar alarm turnoff condition;

(c) means for respectively cyclically coupling control pulses to saidcommon lines respectively having a first and a second predeterminedphase;

(d) means connecting said alarm preparing means in each apartmentbetween one of said common lines and the individual line extending tothe apartment involved for coupling control pulses of said firstpredetermined phase to the associated individual control line only whenthe associated alarm preparing switch is in said alarm preparingcondition;

(e) means for connecting said door switch of each apartment between theother of said common lines and the individual control line extending tothe apartment involved for coupling control pulses of said secondpredetermined phase to the associated individual control lines only whenthe associated door switch is operated to said second condition by theopening of the associated door;

(f) an annunciator means responsive to only the combined presence of thecontrol pulses of said first and second predetermined phase on any ofsaid individual control lines for signalling an alarm for the apartmentinvolved, if such pulses persist after a predetermined delay intervalgreater than said given period which enables an apartment occupantre-entering his own apartment to operate the alarm preparing switch inthe apartment involved to a burglar alarm turn-ofi condition.

20. In a building or the like including a number of sectlons having afirst and a second common line extending therebetween, and an individualline extending to each section of the building, the improvementcomprising a monitoring system for monitoring a given condition in eachsection of the building comprising: a condition sensing switch means foreach section of the building operated to an alarm condition when thecondition to be monitored is present in the associated building section;separate preparing switch means for each section of the building havingan alarm preparing and an alarm disabling condition; control pulsegenerating means for cyclically applying control pulses of a first phaseand polarity to said first common line and control pulses of a secondphase and said polarity to said second common line; isolating rectifiermeans for said common lines; means coupling each of said separatecondition sensing switch means through a different one of said rectifiermeans arranged to pass said control pulses between said rst common lineand the individual control line extending to the associated buildingsection for providing on the individual control line involved controlpulses of said first phase only when the associated condition sensingswitch means is in its alarm condition; means coupling each preparingswitch means through a different one of rectier

1. IN A BUILDING OR THE LIKE INCLUDING A NUMBER OF SECTIONS HAVING A FIRST COMMON LINE EXTENDING THEREBETWEEN AND FORMING PART OF A FIRST COMMON CIRCUIT, A SECOND COMMON LINE EXTENDING BETWEEN SAID BUILDING SECTIONS AND FORMING PART OF A SECOND COMMON CIRCUIT AND AN INDIVIDUAL LINE EXTENDING TO EACH SECTION OF THE BUILDING AND COMPLETING AN INDIVIDUAL CIRCUIT ASSOCIATED WITH THE BUILDING SECTION, AND POWER SUPPLY MEANS FOR PROVIDING ENERGIZING POWER ON SAID COMMON AND INDIVIDUAL LINES FOR SAID CIRCUITS, THE IMPROVEMENT COMPRISING A MONITORING SYSTEM SUPERIMPOSED ON SAID COMMON AND INDIVIDUAL LINES FOR MONITORING A GIVEN CONDITION IN EACH SECTION OF THE BUILDING COMPRISING: A SEPARATE CONDITION SENSING SWITCH MEANS FOR EACH SECTION OF THE BUILDING OPERATED TO AN ALARM CONDITION WHEN THE CONDITION TO BE MONITORED IS PRESENT IN THE ASSOCIATED BUILDING SECTION; A PREPARING SWITCH MEANS FOR EACH SECTION OF THE BUILDING HAVING AN ALARM PREPARING AND AN ALARM DISABLING CONDITION: CONTROL SIGNAL GENERATING MEANS FOR APPLYING A FIRST CONTROL SIGNAL HAVING A FIRST DISTINGUISHING CHARACTERISTIC TO SAID FIRST COMMON LINE AND A SECOND CONTROL SIGNAL HAVING A SECOND DISTINGUISHING CHARACTERISTIC TO SAID SECOND COMMON LINE; MEANS COUPLING EACH OF SAID SEPARATE CONDITION SENSING SWITCH MEANS BETWEEN SAID FIRST COMMON LINE AND THE INDIVIDUAL LINE EXTENDING TO THE ASSOCIATED BUILDING SECTION FOR PROVIDING ON THE INDIVIDUAL LINE INVOLVED SAID FIRST CONTROL SIGNAL ONLY WHEN THE ASSOCIATED CONDITION SENSING SWITCH MEANS IS IN ITS ALARM CONDITION; MEANS COUPLING EACH PREPARING SWITCH MEANS BETWEEN AND SECOND COMMON LINE AND THE INDIVIDUAL LINE EXTENDING TO THE ASSOCIATED BUILDING SECTION FOR PROVIDING ON THE INDIVIDUAL LINE INVOLVED SAID SECOND CONTROL SIGNAL ONLY WHEN THE PREPARING SWITCH MEANS IS IN ITS ALARM PREPARING CONDITION; AND CONTROL SIGNAL RESPONSIVE ANNUNCIATOR MEANS RESPONSIVE ONLY TO THE COMBINED PRESENCE OF SAID FIRST AND SECOND CONTROL SIGNALS ON ANY OF AND INDIVIDUAL LINES FOR SIGNALLING AN ALARM FOR THE SECTION OF THE BUILDING INVOLVED. 